1. Field
The instant invention relates primarily, but is not restricted to, photocopy devices utilizing a visible light source to impress an image upon a photo receptor plate to transfer an image to an unsensitized sheet of paper or other material.
2. Prior Art
Prior art techniques include the major copying processes of xerography, direct electro static and a gelatin transfer process identified as verifax. The xerography process involves the charging of a single drum with electricity. The charged drum is then sensitive to light. The original image is projected upon the drum by shining visible light through the material to be reproduced through a lens onto the drum. Those areas of the drum which are struck by the light lose their electrical charge. Those which are not struck by the light retain their positive electrical charge. The result is a latent electrostatic image on the drum that is a mirror image of the original document. The drum is then cascaded with a black powder, called toner. The powder has a negative charge and adheres to the drum. The image becomes visible on the drum, but is a mirror image of the image to be reproduced. A paper on which the image is to be reproduced is then passed in contact with the drum while charged with electricity. The charge of electricity causes the toner particles to leave the drum and adhere to the paper. At this point the copy is a powder image on the paper but it is not permanent. Thereafter, the image is fused to the paper by melting the powder into the paper.
The direct electrostatic, known in the industry frequently as the electrofax technique, transfers the image directly onto a sensitized copy paper rather than using a sensitized drum as a transfer medium. The paper used in this process is coated with zinc oxide, which acts as a photoconducting material. The zinc oxide coated paper is first given a negative charge in the dark by a corona discharge which makes the paper light sensitive. The paper is then exposed to the image which is projected through a lens system from a visible light source. Light from non-image areas of the document causes the electrical charge on the paper to be dissipated in the corresponding areas. At this point the sensitized paper has a latent, invisible image that is an exact duplicate of the image on the original. The image on the paper can be developed through the use of either a dry or liquid toner. In the dry method of development the developer, consisting of a mixture of pigmented resin powder and iron particles, is applied to the paper by means of a "magnetic brush" which is a magnet that holds the developer mixture. As the brush moves across the paper the positively charged resin powder adheres to the negatively charged image areas of the paper while the iron particles are retained on the magnet. The iron particles are used as a carrier for the resin powder. The paper containing the developed image is then heated for a few seconds to fuse the resin powder to the paper. The image may also be developed by passing it through a liquid developer. The suspended pigment particles cling to the charged areas of the paper by electrostatic attraction and are held to it permanently usually by a resin binder. After most of the liquid developer has flowed off the papers, the remainder is ordinarily removed by blowing warm air across it.
The gelatin transfer method, verifax, uses a light sensitive sheet called a matrix. The matrix consists of paper coated with unhardened gelatin containing a variety of chemicals, one of which is silver halide. The reproduction of images is essentially a photographic phenomenon.